Dimensional Stability of Low Temperature Surface Hardened Stainless Steel Components*

Stainless steels are commonly used for high precision components, which often are exposed to corrosive media. However, their inferior tribological behaviour restrict the use of these materials in many technical applications. Thermochemical surface hardening is one way to overcome these weaknesses. Solution nitriding in the austenitic range above 1000 °C is mainly used for hardening martensitic and ferritic stainless grades. In austenitic and duplex stainless grades, however, the hardening effect is limited. Additionally, the high process temperatures combined with a necessary rapid cooling may lead to non-desired dimensional changes. Low temperature surface hardening processing below 500 °C here offers interesting alternatives for increasing the wear properties, while maintaining the corrosion resistance. This paper demonstrates the influence of high and low process temperatures of thermochemical surface hardening treatments on the tight dimensional tolerances of a rotationally symmetrical precision component made from cold worked AISI 304. Based on these results, current and new industrial applications, which benefit from low temperature surface hardening, will be discussed.

Quenching and Distortion*

This paper is based on a keynote lecture presented by Prof. Fechte-Heinen during the 2nd International Conference on Quenching and Distortion Engineering in April 2021. Firstly, it presents a short summary of the basics of distortion formation. The mechanisms and the potential for distortion with its carriers are discussed in more detail. Furthermore, the method of Distortion Engineering is explained. Finally, selected examples are presented that illustrate the connections between distortion and the quenching process.

Advanced Distortion Analysis of Heat Treated Rings*

The basic approach to interpret distortion as a system property is accepted in science and industry. The determination of significant factors and interactions on distortion in the overall production process of selected components represents a central point to identify relevant distortion mechanisms. In this context, a component specific distortion description is a major step to answer distortion problems. In the field of ball bearing engineering, roundness deviation of raceways is an important characteristic. But this parameter is not useful for distortion engineering because no information concerning ring shape is given. But in literature, roundness deviation can be separated in its respective forms like oval and triangle shape with harmonic analysis. In addition, this analysis can be used to specify an amplitude and a direction in the different shapes to describe distortion. In this article, harmonic analysis is used for advanced distortion analysis of tapered roller bearing. An analysis in graphical form is introduced, which illustrates both the amount and the direction of distortion.

Comparison of the Hardness-Toughness Relationship of Medium-Mn Steels after Q&T and Q&P Treatments*

In contrast to quenching and tempering (Q&T), with quenching to room temperature, quenching and partitioning (Q&P) usually applies quenching to a temperature between Ms and room temperature. To stabilize a sufficient amount of retained austenite (RA), carbon diffusion from martensite into austenite and a prevention of cementite formation takes place during the successive partitioning step. Larger amount of RA, and its transformation into martensite during plastic deformation, provides Q&P treated steels with an enhanced combination of strength and ductility. In this investigation, the effect of different Q&T and Q&P treatments on the hardness-toughness relationship was determined. These results are compared with the RA contents and mechanical properties provided by tensile testing. The obtained results clearly demonstrate that the optimum parameters for strength and ductility do not match with the best combinations of hardness and toughness. Furthermore, the stability of the RA plays an important role in the understanding of toughness properties of the investigated Q&P steels.

In situ Investigation during Low Pressure Carburizing by Means of Synchrotron X-ray Diffraction*

In situ X-ray diffraction investigations during low pressure carburizing (LPC) processes were performed with a specially developed process chamber at the German Electron Synchrotron Facility (DESY) in Hamburg, Germany. Carbon saturation in austenite was reached in less than 20 seconds for all processes with different parameters and carbides formed at the surface. Therefore, the direct contribution of carbon donor gas to the carbon profile after 20 seconds was reduced to very low levels. After that point, further supply of carbon donor gas increased the amount of carbides formed at the surface, which will contribute to the carbon profile indirectly by dissolution in the following diffusion steps. During quenching, martensite at higher temperatures had a lower c/a ratio than later formed ones. This difference is credited to self-tempering effects and reordering of carbon atoms within the martensite lattice.